Backgrounder
Glyphosate: Response to Hairy Cell Leukemia
Allegations
August, 2002
Monsanto Company
A 1998 epidemiologic study from Sweden investigated the potential or suspect occupational
causes of hairy cell leukemia (HCL) (Nordstrom et al., 1998). HCL is a blood cancer that is
manifest as the proliferation of a particular type of white blood cell. It has been classified by
some as a variant non-Hodgkin鈥檚 lymphoma (NHL), while others treat it as a related disorder
with a likely different origin and disease process.
This HCL study preceded the widely publicized NHL and pesticides study from the same
Swedish research group. In addition to agricultural chemicals, this HCL study also considered
exposure to farm animals and numerous other factors (e.g. wood impregnating agents,
petroleum derivatives, 鈥渆xhausts鈥?, ultraviolet light, 鈥渕old dust鈥?, asbestos, etc.). The authors
reported modest but statistically significant associations for all herbicides, all insecticides, all
fungicides, impregnating agents, all animals, all solvents, and paint. Leading experts do not
consider the results of this study to be credible evidence that any of the agricultural factors
studied are causes of HCL. In fact, the study authors themselves recommended that caution be
used when interpreting the results. According to Dr. Mark Cullen of Yale University鈥檚 School of
Medicine: 鈥渢he fact that virtually every tested factor proved positive -- inconceivable biologically -
- speaks to simpler interpretation, namely differential reporting by cases and controls鈥? (Cullen,
1999).
In 2001, the HCL study was reviewed by several experts (Acquavella et al., 2001). These
authors proposed that recall bias was the most likely explanation for the reported findings.
Recall bias refers to the fact that ill people are more likely than well people to recall exposure to
suspected substances. Acquavella et al. conclude: 鈥淚n view of the intrinsically weak measure of
exposure, the multiple hypotheses being tested, the evidence for possible recall bias, the small
numbers of cases and controls with exposure to any herbicide (16 and 22 respectively), and the
inability to control for confounding factors, the validity of reported associations between HCL
and specific agents is questionable.鈥?
The results of the Nordstrom et al. study do not meet well-established criteria from the
epidemiology literature for determining cause and effect. The associations were weak and there
was no dose-response relationship. Finally, there is no experimental evidence from several
long-term studies with animals that support the findings.
There is widespread agreement among regulatory and health organizations that there is no
evidence that glyphosate might cause cancer in people (U.S. Environmental Protection Agency
1993, World Health Organization 1994). These assessments were based on thorough reviews
of numerous toxicology studies conducted according to internationally accepted guidelines. The
most recent review was conducted by the European Commission鈥檚 Health and Consumer
Protection Directorate-General, after which glyphosate was re-registered for use in Europe
(European Commission 2002). The EC review, like others around the world, concluded that
glyphosate is not carcinogenic.
Backgrounder 鈥? Glyphosate: Response to Hairy Cell Leukemia Allegations. 2002. Page 1 of 2
Related Documents: Backgrounder: Glyphosate and Biomonitoring Studies
References
Acquavella JR, Cowell JE, Cullen MR, Farmer DR, Pastides H. (2001) Implications of
Glyphosate Toxicology and Human Biomonitoring Data for Epidemiologic Research. Journal
of Agromedicine 7(4): 7-27.
Cullen MR. (1999) Review of Nordstrom et al., Occupational Exposures, animal exposure and
smoking as risk factors for hairy cell leukemia evaluated in case-control study. Brit. J
Cancer 1998; 77: 2048-2052. Unpublished review.1
European Commission. (2002) Report for the Active Substance Glyphosate, Directive
6511/VI/99, Jan. 21, 2002.
http://europa.eu.int/comm/food/fs/ph_ps/pro/eva/existing/list1_en.htm.
Nordstrom M, Hardell L, Magnuson A, Hagberg H, Rask-Andersen A. (1998) Occupational
exposures, animal exposure and smoking as risk factors for hairy cell leukaemia evaluated in
a case-control study. Brit. J Cancer 77(11): 2048-2052.
U.S. Environmental Protection Agency. (1993) Reregistration Eligibility Decision (RED):
Glyphosate. EAP-738-F-93-011, September 1993, Washington, DC.
http://www.epa.gov/oppsrrd1/REDs/factsheets/0178fact.pdf
World Health Organization. (1994) Glyphosate. Environmental Health Criteria No. 159. World
Health Organization, Geneva, Switzerland.
http://www.inchem.org/documents/ehc/ehc/ehc159.htm
1
Unpublished references can be requested from Monsanto鈥檚 Public Affairs Director for Agricultural
Chemicals at 314-694-3546.
Backgrounder 鈥? Glyphosate: Response to Hairy Cell Leukemia Allegations. 2002. Page 2 of 2
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